This invention relates to internal combustion engines for propelling motor vehicles, and more particularly to a strategy for controlling an engine brake that has a hydraulic actuator that is actuated during braking.
When it is desired to slow a motor vehicle being propelled by an internal combustion engine, the driver typically releases the accelerator pedal. That action alone will cause the vehicle to slow due to various forces acting on the vehicle. Driver action may also include applying the vehicle service brakes, depending on the amount of braking needed.
A known method for retarding the speed of a running internal combustion engine in a motor vehicle without necessarily applying the service brakes comprises increasing engine back-pressure, and in a motor vehicle, a temporary increase in engine back-pressure can be effective to aid in decelerating the vehicle provided that the vehicle drivetrain is keeping the driven wheels coupled to the engine. With the accelerator pedal released, engine fueling diminishes, or even ceases. Instead of flowing toward the driven wheels, the power flow through the drivetrain reverses direction, with the kinetic energy of the moving vehicle now being dissipated by operating the engine as a pump.
Any of various known engine brakes and methods may be used to temporarily increase engine back-pressure in order to retard the speed of a moving motor vehicle. Regardless of the particular type of engine brake, an actuator is typically present in the braking mechanism A hydraulic actuator is one example.
Certain diesel engines have fuel injection systems that utilize hydraulic fluid, or oil, under pressure to force fuel into engine combustion chambers. The hydraulic fluid is supplied from a hydraulic rail, or oil rail, to a respective fuel injector at each engine cylinder. When a valve mechanism of a fuel injector is operated by an electric signal from an engine control system to inject fuel into the respective cylinder, the hydraulic fluid is allowed to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber. The hydraulic fluid is delivered to the rail by a pump, and as an element of the fuel injection control strategy executed by the engine control system, the hydraulic pressure in the oil rail is regulated to provide an appropriate injection control pressure (ICP).
A hydraulic actuator in an engine brake system can take advantage of the already available source of hydraulic fluid, or oil, in the oil rail. But because ICP in the oil rail is controlled by the fuel injection control strategy that is embedded in the engine control system (ECS), the inclusion of a brake control pressure (BCP) strategy in an ECS needs to address implications of using ICP for engine brake actuation. Likewise, use of ICP for actuating the engine brake may have implications on the fuel injection control strategy.
Excessively high ICP may be undesirable in an engine brake system A malfunction in a BCP valve that controls the delivery of hydraulic fluid to a hydraulic actuator of an engine brake system may cause the BCP valve to stay open when it should close so that ICP will not be removed from the actuator when it should. That could be a source of potential damage to the engine.
Hence, the ability of a BCP strategy to utilize ICP requires a proper interaction between the BCP strategy and the ICP strategy.
An important aspect of the present invention involves an engine control system strategy that provides a novel BCP strategy for a hydraulic-actuated engine brake and that properly interrelates a BCP strategy and an ICP strategy so that brake application can take advantage of hydraulic fluid, or oil, that is used for operating engine fuel injectors while guarding against the possibility that the use of ICP might damage the engine in the unexpected event that unintended pressures are applied to the actuator.
Accordingly, one generic aspect of the present invention relates to an internal combustion engine comprising a fueling system for forcing fuel into engine combustion chambers where the fuel is combusted to power the engine and an exhaust system through which exhaust gases generated by combustion of fuel in the combustion chambers pass from the engine. An engine brake system is associated with the exhaust system to brake the engine by controlling exhaust flow during engine braking and comprises one or more hydraulic actuators that is or are actuated during braking of the engine by the engine brake system.
A hydraulic system supplies hydraulic fluid under pressure both to the fueling system for forcing fuel into the combustion chambers and to the one or more actuators. A control system controls various aspects of engine operation, including controlling braking of the engine by selectively communicating hydraulic fluid to the one or more actuators.
A fuel injection control strategy in the control system provides closed-loop control of injection control pressure to cause injection control pressure to correspond to a desired injection control pressure set by the fuel injection control strategy.
A brake control pressure strategy in the control system signals hydraulic pressure supplied to the one or more actuators in excess of a pressure determined by the brake control pressure strategy and imposes limitation on injection control pressure when such excess pressure is signaled.
Another aspect of the invention relates to the control system just described.
Still another aspect relates to a method of control of pressure of hydraulic fluid that serves both engine fuel injectors and one or more actuators of an engine brake.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.